The incidence of community-acquired Clostridium difficile infection (CA-CDI) has increased globally. Clinically important C. difficile strains have been isolated from retail foods in Europe and United States, with prevalence ranging up to 42%. In Australia, a recent study has found a high prevalence of C. difficile on Australian retail vegetables. Many of the isolates were strains known to cause diarrhoea in humans and livestock. We suspect that the soil in crop farming might be contaminated with C. difficile. In Australia, human biosolids (treated sewage sludge) are composted for agricultural use; animal manures are used as soil conditioners without composting, and food waste from supermarkets are recycled using anaerobic digestion to produce an organic liquid fertiliser which is added to a range of garden products due to its nutritional value and level of living microorganisms. In this study we investigated the prevalence and genotypes of C. difficile in garden products.
Human biosolids, organic liquid fertiliser and retail garden products were collected, selective and enrichment culture was performed and isolates were characterized by PCR toxin gene profiling and ribotyping.
C. difficile was isolated from 26.8% (22/82) samples overall; human biosolids, 75.0% (3/4), organic liquid fertiliser, 50.0% (3/6); retail soil conditioners, 29.7% (11/37); retail mulches, 16.7% (2/12); retail garden mixes, 13.6% (3/22) and retail organic fertilizer, 0.0% (0/1). Almost half the isolates (45.9%, 17/37) were toxigenic. Ribotyping revealed 24 different types, including UK 014/020, the most prevalent strain in humans and piglets in Australia; UK 237, a pig strain that is unique to a piggery in Western Australia and UK 056, the equal third most prevalent strain in humans, piglets, sheep and lambs.
Some of the ribotypes detected are known to cause disease in humans and Australian livestock. Soil and garden products contaminated with C. difficile might be responsible for the high prevalence of C. difficile in Australian retail vegetables, which in turn may be contributing to the rise in incidence of CA-CDI.